The present invention relates to heat curable compositions resulting from the use of a platinum catalyst, a norbornane or norbornene silicone block copolymer and a polyfunctional reactive organosilicon material capable of undergoing an .tbd.SiH to .tbd.SiC.sub.2 H.sub.3 addition reaction with the norbornane or norbornene silicone block copolymer.
Prior to the present invention, room temperature vulcanizable polydiorganosiloxanes, for example, silanol terminated polydimethylsiloxanes were available in either one-package or two-package systems based on the type of moisture sensitive cross-linking agents utilized in the composition. A typical one-package system is based on the use of methyltriacetoxysilane and a silanol terminated polydimethylsiloxane as shown by Ceyzeriat, U.S. Pat. No. 3,133,891. A two-package system as shown by Nitzsche et al, U.S. Pat. No. 3,065,194 requires the blending of silanol terminated polydimethylsiloxane with a curing catalyst, such as ethyl orthosilicate in combination with dibutyltindilaurate. The two package system requires mixing of the curing catalyst with the silanol terminated polydimethylsiloxane prior to use.
The above described one-package and two-package room temperature vulcanizable compositions generally require the use of reinforcing filler, for example, a silica filler in amounts of from 5-300 parts, per 100 parts of silicone polymer, if improved tensile strength to the resulting cured silicone is desired. Another procedure available to improve the toughness of the cured silicone polymers is the introduction of silarylenesiloxy units into the polymer chain to produce a copolymer consisting essentially of diorganosiloxy units chemically combined with silarylenesiloxy units. Although these procedures substantially enhance the modulus (psi) of the silicone polymer, these procedures are uneconomic or do not achieve the degree of toughness based on elongation (%) x tensile (psi) desired in the end product.
In my copending application Ser. No. 567,609, filed Jan. 3, 1984, for Silicone-Polyimide Copolymers, Condensation Vulcanizable Compositions Obtained Therefrom and Method for Making, silicone-polyimide copolymers are described having terminal silanol or silicon hydride radicals based on the use of a norbornene terminated polyimide. A hydrosilation reaction is employed to introduce silicon-hydrogen onto the terminal norbornene groups of the polyimide. The resulting hydrosilyl terminated polyimide is reacted with silanol terminated polydiorganosiloxane in the presence of a catalyst to produce silanol terminated polydiorganosiloxane-polyimide copolymer. Room temperature or low temperature condensation vulcanizable compositions based on the use of such silanol-terminated copolymers provide cured silicone-polyimide copolymers exhibiting improved toughness.
In my copending application Ser. No. 604,569, Heat Curable Silicone-Polyimide Block Copolymers, filed on Apr. 27, 1984, a free radical initiator such as an organic peroxide is found useful in effecting the thermal cure of a norbornene, or norbornane polydiorganosiloxane which can have chemically combined .tbd.SiC.sub.2 H.sub.3 units.
The present invention is based on the discovery that heat curable silicone-polyimide compositions convertible to high strength elastomers also can be made by using an effective amount of a platinum catalyst to effect a polyaddition reaction between a polyfunctional organosilicon material, for example, an organosilane or organosiloxane fluid, and a norbornane or norbornene silicone block copolymer defined hereinafter having chemically combined .tbd.SiC.sub.2 H.sub.3 or .tbd.SiH units. For example, a mixture of polyvinylarylsilane or vinyl containing polydiorganosiloxane and a silicon hydride terminated polyimide having the formula, ##STR1## can be readily vulcanized with a platinum catalyst at a temperature of from about 25.degree. C. to about 250.degree. C., where R--R.sup.8, Y, Q, and n are as defined below, and r has a value of 0 to 2000 inclusive.
Alternatively, a vinyl terminated silicon-polyimide block polymer of the formula ##STR2## can be vulcanized with a silicon hydride, as defined hereinafter, in the presence of an effective amount of a platinum catalyst, where R.sup.7 is defined below, R.sup.9 is CH.sub.2 CH.sub.2, m is an integer having a value of 1 to 100, x is an integer having a value of 1 to 10.sup.4, and G is a divalent group formed by reacting a silicon hydride terminated polyimide of formula (1) with a vinyl terminated polydiorganosiloxane of the formula, ##STR3##
The resulting silicone polyimide elastomeric copolymers exhibit improved tensile strength (psi) as compared to conventional room temperature vulcanized or organic peroxide cured organopolysiloxane elastomers.